The present invention relates to a screwer test bench and in particular to a bench with an innovative braking device for resisting torque simulation.
In the prior art, screwer test benches are well known. Such benches simulate the resisting torque of a screw in tightening and at the same time measure the parameters of torque and angle developed by a screwer applied to the bench and signal deviations of said parameters from a predetermined characteristic curve.
In such benches correct simulation of resisting torque is the most critical part in order that the measurements made be truly representative of the operation of the screwer in normal use.
In accordance with a known system the bench comprises a cap with which is engaged the screwer being tested. A friction disk is thrust against the cap to produce the braking force.
Known systems are based on brake types realized in accordance with the engineering teachings for normal brakes used for stopping rotating shafts such as the brakes used in wheeled vehicles. In these brakes it is important however to have adequate overall braking force upon brake operation without interest for any small braking force oscillations around the mean value during the braking action. In practice, in these known brakes care is had only that the braking force oscillations around the mean value not reach a value such as to produce vibrations noticeable to the vehicle user. In addition, any differences in the friction coefficient are readily compensated for by a greater pressure by the user on the brake.
The holder of this application has noted however that in known systems small oscillations or tripping of the brakes used are generated which are in good part due to the differences between static and dynamic friction and generate effects which are absolutely imperceptible and without influence in a braking system whose purpose is merely to stop rotation of a shaft but which are absolutely harmful in a measurement system such as that of screwer test benches while introducing errors in the measurement of the performance of screwers subjected to testing and especially near stopping.
The general purpose of the present invention is to remedy the above mentioned shortcomings by making available a screwer test bench equipped with an innovative friction brake which would be free of those oscillation and tripping problems which make measurement inaccurate.
In view of this purpose it was sought to provide in accordance with the present invention a screwer test bench comprising a coupling designed for coupling with the head of a screwer and connected to a controlled braking unit and a sensor unit for detection of mechanical magnitudes transmitted between the coupling and the braking unit characterized in that the braking unit comprises a brake with carbon friction surfaces in an oil bath.